Organic electroluminescent device and method for fabricating the same

ABSTRACT

An organic electroluminescent device and a method for fabricating the same are disclosed. A first electrode, which is a pixel electrode, and a second electrode, which is a common electrode, are formed to have an uneven surface, thereby maximizing a luminous efficiency and a reflection efficiency. In addition, since a surface of a contact area between a counter electrode and a common electrode can be increased, the resistivity between the two electrodes can be reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Application Nos.P2003-029047, filed on May 7, 2003, and P2003-040713, filed on Jun. 23,2003, which are hereby incorporated by reference as if fully set forthherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electroluminescent device, and moreparticularly, to an active matrix electroluminescent device and a methodfor fabricating the same.

2. Discussion of the Related Art

An electroluminescent device is being viewed as a next generation flatdisplay device for its characteristics of a wide viewing angle, a highaperture ratio, and a high chromaticity. More specifically, in anorganic electroluminescent (EL) device, when an electric charge isinjected into an organic luminescent layer formed between a holeinjection electrode and an electron injection electrode, the electronand the hole are paired to each other generating an exciton, the excitedstate of which falls to a ground state, thereby emitting light. Thus,the organic electroluminescent device (ELD) can be operated at a lowervoltage, as compared to other display devices.

Depending upon the driving method, the organic ELD can be classifiedinto a passivation ELD and an active matrix ELD. The passivation ELD isformed of a transparent electrode on a transparent substrate, an organicEL layer on the transparent electrode, and a cathode electrode on theorganic EL layer. The active matrix ELD is formed of a plurality of scanlines and data lines defining a pixel area on a substrate, a switchingdevice electrically connecting the scan lines and the data lines andcontrolling the electroluminescent device, a transparent electrodeelectrically connected to the switching device and formed in the pixelarea on the substrate, an organic EL layer on the transparent electrode,and a metal electrode on the organic EL layer. Unlike the passivationELD, the active matrix ELD further includes the switching device, whichis a thin film transistor (TFT).

However, the related are active matrix ELD is disadvantageous in thatthe thin film transistor causes a decrease in the aperture ratio and theluminous efficiency of the device. An expansion of the pixel area isrequired in order to enhance the aperture ratio and the luminousefficiency. However, there are limitations to such expansion. Morespecifically, an excessive expansion of the pixel area causes deficiencyin the functions of the thin film transistor, the counter electrode, andthe metal electrode.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an organicelectroluminescent device and a method for fabricating the same thatsubstantially obviate one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide an organicelectroluminescent device and a method for fabricating the same thatenhances the luminous efficiency and improves the electrical function ofthe device, simultaneously.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, anorganic electroluminescent device includes a substrate including a thinfilm transistor having a pixel area defined thereon, a planarizedinsulating layer formed on the thin film transistor and substrate, afirst electrode formed on the planarized insulating layer and having aplurality of uneven patterns, an electroluminescent layer formed on thefirst electrode, and a second electrode formed on the electroluminescentlayer.

Herein, the planarized insulating layer has a plurality of unevenpatterns on the pixel areas and a contact hole on the thin filmtransistor. Also, the electroluminescent layer and the second electrodehave a plurality of uneven patterns on the pixel area.

The organic electroluminescent device further includes an insulatinglayer formed on a predetermined portion of the first electrode on aboundary area of the pixel area and having a projected part projectinginto the pixel area, and a counter electrode formed on the insulatinglayer and having a projected part in the pixel area.

In another aspect of the present invention, a method for fabricating anorganic electroluminescent device includes forming a thin filmtransistor on a substrate and having a pixel area defined thereon,forming a planarized insulating layer having a plurality of unevenpatterns on an entire surface of the thin film transistor and substrate,forming a first electrode having a plurality of uneven patterns on theplanarized insulating layer, forming an electroluminescent layer on thefirst electrode, and forming a second electrode on theelectroluminescent layer.

Herein, the forming a planarized insulating layer having a plurality ofuneven patterns includes depositing an insulating material layer on anentire surface of the thin film transistor and substrate, forming aplurality of patterns having pillar shapes on the insulating materiallayer, and heat-treating the insulating material layer. In addition, thepatterns having pillar shapes are formed to be spaced apart from oneanother to have a predetermined gap and formed to have a predeterminedwidth.

The method for fabricating the organic electroluminescent device furtherincludes forming an insulating layer on a predetermined portion of thefirst electrode at a boundary area of the pixel area and having anextended part into the pixel area, and forming a counter electrode onthe insulating layer including the extended part.

In another aspect of the present invention, an organicelectroluminescent device includes a substrate including a thin filmtransistor having a pixel area defined thereon, a first insulating layerformed on the thin film transistor and substrate, a first electrodeformed on the first insulating layer, a second insulating layer formedon a predetermined portion of the first insulating layer excluding thepixel area and having a projected part at the pixel area, a counterelectrode formed on the second insulating layer having a projected partat the pixel area, an electroluminescent layer formed on the firstelectrode at the pixel area, and a second electrode formed on theelectroluminescent layer and the counter electrode.

Herein, the first insulating layer has a plurality of uneven patterns atthe pixel area and a contact holes on the thin film transistor.Additionally, the electroluminescent layer and the second electrode havea plurality of uneven patterns. Also, the electroluminescent layer isformed only at the pixel area excluding the projected part of thecounter electrode.

In a further aspect of the present invention, a method for fabricatingan organic electroluminescent device includes forming a thin filmtransistor on a substrate and having a pixel area defined thereon,forming a first insulating layer on an entire surface of the thin filmtransistor and substrate, forming a first electrode on the firstinsulating layer, forming a second insulating layer on a predeterminedportion of the first electrode excluding the pixel area and including aprojected part in the pixel area, forming a counter electrode having aprojected part in the pixel area on the second insulating layer, formingan electroluminescent layer on the first electrode, and forming a secondelectrode on the electroluminescent layer.

Herein, the first electrode, the electroluminescent layer, and thesecond electrode have a plurality of uneven patterns.

In the method for fabricating the organic electroluminescent deviceaccording to the present invention, a shadow mask having a plurality ofpatterns formed in the same shape as the projected part of the secondinsulating layer is used to form the electroluminescent layer. Herein,the electroluminescent layer is formed only on the pixel area excludingthe projected part of the counter electrode.

Finally, the method for fabricating the organic electroluminescentdevice according to the present invention further includes forming aplurality of uneven patterns and a contact hole on the first insulatinglayer. Herein, a plurality of patterns having pillar shapes are formedand heat-treated on the first insulating layer for forming a pluralityof uneven patterns on the first insulating layer.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings;

FIGS. 1A to 1I illustrate cross-sectional views showing the processsteps of a method for fabricating an organic electroluminescent deviceaccording to the present invention;

FIG. 2 illustrates a plane view showing the size of and distance betweeneach contact hole formed on a planarized layer according to the presentinvention;

FIG. 3 illustrates a plane view of the contact holes according toanother embodiment of the present invention;

FIGS. 4 to 7 illustrate the method for fabricating the organicelectroluminescent device according to the present invention;

FIG. 8 illustrates a shadow mask according to the present invention; and

FIGS. 9 to 11 illustrate the method for fabricating the organicelectroluminescent device according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIGS. 1A to 1I illustrate cross-sectional views showing the processsteps of a method for fabricating an organic electroluminescent deviceaccording to the present invention.

Referring to FIG. 1A, in order to use the glass substrate 10 as anactive layer of a thin film transistor 200, a semiconductor layer isdeposited by using a polycrystalline silicon. Then, the semiconductorlayer is patterned, so as to leave an area whereby the thin filmtransistor 200 is to be formed in a later process. Subsequently, a gateinsulating layer 12 is deposited on the entire surface of the substrate10 and the patterned semiconductor layer 11, 11 a, and 11 b, and aconductive layer is deposited thereon, so as to form a gate electrode.The conductive layer is patterned so that only a predetermined area onthe patterned semiconductor layer 11, 11 a, and 11 b remains, therebyforming the gate electrode 13.

Thereafter, the gate electrode 13 is used as a mask to injectimpurities, such as boron (B) or phosphor (P), into the semiconductorlayer 11 a and 11 b. Then, after a heat-treating process, source anddrain areas 11 a and 11 b are formed on the thin film transistor 200. Inaddition, the area of the semiconductor layer having no impuritiesinjected therein becomes a channel area 11. Herein, since the gateelectrode 13 is used as a mask to inject impurities, the boundaries ofthe source and drain areas 11 a and 11 b and the channel area 11 arealigned with each edge of the gate electrode 13.

A first interlayer dielectric 14 is formed on the insulating layer 12and the gate electrode 13. The first interlayer dielectric 14 and thegate insulating layer 12 are selectively etched to expose apredetermined portion of the upper surface of the source and drain area11 a and 11 b, so as to form a contact hole. Then, the contact hole isfilled with metal, thereby forming a plurality of electrode lines 15each electrically connected to the source and drain area 11 a and 11 b.Subsequently, a second interlayer dielectric 16 is formed on the firstinterlayer dielectric 14 and the electrode lines 15. Herein, the formingof the second interlayer dielectric 16 can be omitted.

Referring to FIG. 1B, in order to form a planarized insulating layer 17on the second interlayer dielectric 16, an insulating material isdeposited on the second interlayer dielectric 16 through a spin-coatingmethod, which is then hardened by a pre-baking process.

Subsequently, as shown in FIG. 1C, by using a mask 18 having a set ofpatterns spaced apart from one another, the planarized insulating layer17 is exposed to UV light rays. And, by using a developing solution, theplanarized insulating layer 17 is developed, so as to form a set ofpatterns 17 a spaced apart from one another, as shown in FIG. 1D. Inareas having no patterns 17 a, the surface of the second interlayerdielectric 16 is exposed.

FIG. 2 illustrates a plane view of the patterns according to anembodiment of the present invention. Referring to FIG. 2, the patterns17 a of the planarized insulating layer 17 are formed in the shape ofsquare pillars. The patterns 17 a can also be formed in other shapes, asshown in FIG. 3. The shapes can range from pillars having polygonalshapes of more than three end-points, oval shapes, round shapes, and soon. The patterns 17 a are formed to be spaced apart at a set distance,the width and gap of which are less than 1 centimeter (cm) (i.e., 0≦a≦1cm, 0≦b≦1 cm, 0≦c≦1 cm, 0≦d≦1 cm).

Referring to FIG. 1E, patterns having uneven shapes are formed on thesurface of the planarized insulating layer 17 through a melt-bakingprocess. At this point, when the baking process is carried out a lowtemperature, which prevents the planarized insulating layer 17 fromhardening, the patterns 17 a melt and leak, thereby being deformed aspatterns with uneven shapes. Subsequently, the planarized insulatinglayer 17 and the second interlayer dielectric 16 are selectively etchedto expose the electrode line 15 connected to the drain area 11 b of thethin film transistor 200, thereby forming a plurality of contact holes18.

Thereafter, as shown in FIG. 1F, a first electrode 19 is formed on theentire surface of the contact holes 18 and the planarized interlayerdielectric 17. In a bottom-emission EL device, the first electrode 19 isformed of a transparent substance, such as ITO. Conversely, in atop-emission EL device, the first electrode 19 is formed of a metal withhigh reflexibility and high work function, such as chrome (Cr), copper(Cu), tungsten (W), gold (Au), nickel (Ni), silver (Ag), titanium (Ti),tantalum (Ta), or an alloy of any of the same. The metals can also bedeposited in multi-layered forms. The first electrode 19 deposited onthe inner surface of the contact hole 18 is connected to the electrodeline 15 at the lower portion of the contact hole 18. The first electrode19 deposited on the planarized insulating layer 17 has uneven shapedpatterns similar to those of the planarized insulating layer 17. Asdescribed above, due to the uneven surface of the first electrode 19 atthe pixel area, the reflection efficiency can be enhanced.

Moreover, the first electrode 19 is selectively removed, so as toelectrically divide the pixel areas, and the first electrode becomes aplurality of pixel electrodes 19 (i.e., anodes) being electricallyconnected to the drain area 11 b through the electrode line 15.

Referring to FIG. 1G, an insulating layer 20 is formed on the areaexcluding the pixel areas. The insulating layer 20 embeds the planarizedinsulating layer 17 and the pixel electrodes 19 located at the boundaryarea inbetween the pixel areas.

As described above, the insulating layer 20 overlaps a portion of thepixel electrode. Herein, as the area of the insulating layer 20overlapping the pixel electrode 19 becomes larger, the pixel areasbecome smaller. Therefore, in order to increase the aperture ratio ofthe device, the overlapping area should be minimized during thefabrication process. However, when the overlapping area is excessivelynarrow, the contacting area between a counter electrode 21 and a secondelectrode 23 also becomes narrow, thereby increasing the risk of a shortcircuit. In order to resolve such problems, the insulating layer 20according to the present invention has a projected part 20 a projectinginto a pixel area 100, as shown in FIGS. 4 and 5, so as to increase theaperture ratio and expand the contact area between the counter electrode21 and the second electrode 23. Herein, the projected part 20 a can beformed over the thin film transistor 200, or the projected part 20 a canbe formed in the pixel areas 100. The insulating layer 20 is extendednot only to the upper portion of the boundary area between the pixelareas 100, but also to a portion of the pixel areas 100, therebyexpanding the contact area between the counter electrode 21 and thesecond electrode 23.

Additionally, as shown in FIGS. 6 and 7, the counter electrode 21 isformed on the insulating layer 20. The counter electrode 21 is formed onthe boundary area between the pixel areas 100, just as the insulatinglayer 20. On the other hand, the counter electrode 21 may also be formedon the projected part 20 a of the insulating layer 20. Accordingly, ahigh aperture ratio of the device can be maintained and the surface areaof the counter electrode 21 can be expanded, simultaneously. In order toprevent the contact between the counter electrode 21 and the pixelelectrodes 19, the counter electrode 21 should be formed on apredetermined portion of the insulating layer 20, so as to expose theinsulating layer 20 on the periphery of each pixel areas, and not on theentire surface of the insulating layer 20. The counter electrode 21 isformed of a metal having low resistivity, such as any one of chrome(Cr), aluminum (Al), copper (Cu), tungsten (W), gold (Au), nickel (Ni),silver (Ag), and neodymium (Nd), or the alloy of any of the same. Morespecifically, when using a metal low in transparency, such as chrome(Cr), as the counter electrode 21, the metal can also act as a blackmatrix blocking light.

Referring to FIGS. 1H and 11, an organic electroluminent (EL) layer 22is formed on the pixel electrodes 19 by using a shadow mask 30. Theorganic EL layer 22 is deposited only on the pixel areas 100. Theorganic EL layer 22 is formed of a hole transport layer (not shown), aemission layer (not shown), and an electron transport layer (not shown)serially deposited onto one another. In order to prevent the organic ELlayer 22 from being deposited on the projected part 21 a of the counterelectrode 21, a plurality of patterns of the shadow mask 30 completingthe active matrix organic electroluminescent device according to thepresent invention.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents. each has a projected part 30 asimilar to the projected part 20 a of the insulating layer 20, as shownin FIG. 8.

FIGS. 9 and 10 illustrate the shadow mask 30 according to otherembodiments of the present invention. Referring to FIG. 9, whendepositing the organic EL layer 22, the patterns of the shadow mask 30should be aligned with the pixel areas 100. And, the projected parts 30a of the patterns should be aligned with the projected part 20 a of theinsulating layer 20. The organic EL layer 22 is formed in the order ofthe colors red (R), green (G), and blue (B). By using the shadow mask30, a red emission material, a green emission material, and a blueemission material are serially deposited. The shadow mask 30 is alsoused when depositing a common material of each of the R, G, and Borganic EL layers 22.

As shown in FIG. 1H, the second electrode 23 is deposited on the exposedportion of the insulating layer 20, the counter electrode 21, and theorganic EL layer 22. In the top-emission EL device, the second electrode23 is formed of a transparent conductive material, such as indium tinoxide (ITO) or indium zinc oxide (IZO). On the other hand, in thebottom-emission EL device, the second electrode 23 is formed of a metalhaving high reflectivity. In the top-emission EL device, in order toform the second electrode 23, an aluminum layer having a thickness ofseveral nanometers (nm) and either a silver layer having a thickness inthe range of several to several tens of nanometers (nm), or a metal of aMg_(x)Ag_(x-1) group having a thickness in the range of several toseveral tens of nanometers (nm), are serially deposited on the entiresurface of the exposed portion of the insulating layer 20 and theorganic EL layer 22.

Finally, referring to FIG. 1I, a protective layer 25 is formed toprotect the organic EL layer 22 from oxygen or moisture. Subsequently,although not shown in the drawings, a protective cap is mounted thereonby using a sealant and a transparent substrate, thereby

1-24. (canceled)
 25. An organic electroluminescent device comprising: asubstrate having a pixel area provided thereon; a first insulating layerhaving an uneven pattern formed on the substrate; a first electrodeformed on a first predetermined portion of the first insulating layer; asecond insulating layer formed on a second predetermined portion of thefirst insulating layer; a counter electrode formed on a non-pixel areaother than the pixel area, the counter electrode to overlap the secondinsulating layer; an electroluminescent layer formed on the firstelectrode; and a second electrode formed on the electroluminescentlayer.
 26. The device of claim 25, wherein the uneven pattern comprisesa plurality of patterns spaced apart from one another by a gap of lessthan 1 cm.
 27. The device of claim 25, wherein the uneven patterncomprises a plurality of patterns having a width of less than 1 cm. 28.The device of claim 25, wherein the uneven pattern comprises a pluralityof round shapes.
 29. The device of claim 25, wherein at least one of thesecond insulating layer and the counter electrode includes a projectedpart to project into the pixel area.
 30. The device of claim 25, whereinthe electroluminescent layer is formed only at the pixel area excludinga vicinity of a corner of the pixel area.
 31. The device of claim 25,wherein the first electrode comprises a transparent substance.
 32. Thedevice of claim 25, wherein the first electrode comprises a metal. 33.The device of claim 25, wherein the first electrode comprises an anode.34. The device of claim 25, wherein the second electrode comprises atransparent conductive material.
 35. The device of claim 25, wherein thesecond electrode comprises a metal.
 36. The device of claim 25, whereinthe first electrode, the electroluminescent layer and the secondelectrode have the uneven pattern.
 37. An organic electroluminescentdevice comprising: a substrate having a pixel area; a first electrodeformed on the pixel area; a first insulating layer formed on apredetermined portion of the substrate and having an uneven pattern; acounter electrode formed at a non-pixel area, the counter electrode tooverlap the first insulating layer; an electroluminescent layer formedon the first electrode; and a second electrode formed on theelectroluminescent layer.
 38. The device of claim 37, wherein the unevenpattern comprises a plurality of patterns spaced apart from one anotherby a gap of less than 1 cm.
 39. The device of claim 37, wherein theuneven pattern comprises a plurality of patterns having a width of lessthan 1 cm.
 40. The device of claim 37, wherein the uneven patterncomprises a plurality of round shapes.
 41. The device of claim 37,further comprising a second insulating layer formed on a portion of thefirst insulating layer.
 42. The device of claim 41, wherein the counterelectrode further overlaps the second insulating layer.
 43. The deviceof claim 41, wherein at least one of the second insulating layer and thecounter electrode includes a projected part to project into the pixelarea.
 44. The device of claim 37, wherein the first electrode, theelectroluminescent layer and the second electrode have the unevenpattern.
 45. An organic electroluminescent device comprising: asubstrate having a pixel area; a first insulating layer having an unevenpattern on the substrate; a first electrode on a first predeterminedportion of the first insulating layer; a second insulating layer on asecond predetermined portion of the first insulating layer; a counterelectrode on a non-pixel area and on a portion of the pixel area, thecounter electrode to overlap the second insulating layer; anelectroluminescent layer on the first electrode; and a second electrodeformed on the electroluminescent layer.
 46. The device of claim 45,wherein the uneven pattern comprises a plurality of patterns spacedapart from one another by a gap of less than 1 cm.
 47. The device ofclaim 45, wherein the uneven pattern comprises a plurality of patternshaving a width of less than 1 cm.
 48. The device of claim 45, whereinthe uneven pattern comprises a plurality of round shapes.
 49. The deviceof claim 45, wherein the second insulating layer includes a projectedpart to project into the pixel area.
 50. The device of claim 49, whereinthe counter electrode is provided on the projected part.
 51. The deviceof claim 45, wherein the first electrode, the electroluminescent layerand the second electrode have the uneven pattern.